An asylum seeker whose boat was turned back to Indonesia by Australia has given the ABC a detailed first-person account alleging he was deliberately burned by Australian military personnel while in their custody.

It is the first time any of the three alleged victims of the January incident, on a fishing boat called the Riski, has given their version of events.

The account of Mustafa Ibrahim, a 23-year-old Sudanese asylum seeker, and other evidence found by 7.30's investigation raise new questions about the turn-back of the boat by the military between January 1 and January 6.

The Australian Government has said allegations that people were deliberately burned on the boat were "baseless" and "unsubstantiated".

Read statements to 7.30 from:

The ABC has established that a distress call was made from the boat shortly before it was turned back.

Two Somali passengers interviewed by 7.30 each described losing a brother overboard during rough weather when closing on the Australian coast, just hours before they were intercepted and turned back to Indonesia.

One of them has called on the Australian Government to provide information about his brother's whereabouts or release his body.

Customs today told the ABC that Australian authorities had interviewed the master of the asylum seekers' boat, who told them no-one had gone overboard.

The agency also said the weather had been "benign" at the time of the alleged incident.

"Notwithstanding this assessment, and as a precaution, the Australian authorities on scene conducted an extensive search by air and sea of the local area and did not locate any person from the vessel," a spokesman for the Operation Sovereign Borders Joint Agency Task Force said.

One of the passengers, Somali Saed Yislam, told the ABC that before the boat was intercepted, he and his brother had been sleeping together on the top deck when he heard a "whoosh" sound as his brother fell in the water.

"I screamed, I screamed I screamed, the man did not stop the boat," he said.

7.30 spoke to 12 passengers from the boat in two detention centres at opposite ends of Indonesia. Five of them claimed they had either been involved in the burns incident or had seen it. Two others said they heard screams.

Data downloaded from it provides detailed information about the boat's more than 2,000-kilometre round trip from Indonesia to Australia and back again.

It shows the boat made it to within eight kilometres of Australia's Melville Island, north of Darwin, and was heading ashore at 12 kilometres per hour.

Passengers claim they landed on a beach soon after, and were quickly rounded up by military personnel despatched from a Navy ship and forced back on their boat.

The Australian Government has never acknowledged that the boat came ashore.

At the end of January, Immigration Minister Scott Morrison claimed there had been no boat arrivals since mid-December.

Passengers describe rising tension culminating in protest

During the ensuing ocean voyage under Navy escort, passengers have described rising tension and a breakdown of discipline on board as it became clear they were being returned to Indonesia, culminating in a "strike" or "protest" during which several men jumped in the water.

Passengers said the "Army" or "soldiers" had instituted a rule by which the asylum seekers could only use the toilet once in 24 hours, men during the day and women at night.

They admit there had been a previous attempt to sabotage the engine and said they had assumed the ban on accessing the wheelhouse and toilet – located beyond, in the stern – was to keep them away from it.

And they argued with me and they told me not to go ... Then they brought me, one came out this side the other one came out the other side and they put my hand on the exhaust

Mustafa Ibrahim

But the restriction infuriated the passengers, and when a Somali woman with three children had been blocked from accessing the toilet, four men staged a violent protest.

Passengers said the first man to enter the wheelhouse had been a Somali, Bobies Nooris, who was immediately pepper-sprayed by one of the Australian personnel.

Mr Nooris admits he then burned himself accidentally on the engine exhaust while stumbling around, blinded.

He claimed he had only been trying to recover some belongings from the wheelhouse near the engine, but other passengers said he had led the protest.

Mr Ibrahim told the ABC he had also tried to get access to the toilet but Australian military personnel had refused, prompting a confrontation.

"I came to the toilet area and I met those people near the door. There were nearly six people at the door," he said.

"Two people came and met me and then I pointed that I wanted to urinate. I could not speak English so I show them I want to urinate.

"And they argued with me and they told me not to go and then one of them held me from this side and another from this side. Then they brought me, one came out this side the other one came out the other side and they put my hand on the exhaust."

Asylum seeker describes men being deliberately burned

Asked if it could have been an accident, Mr Ibrahim said Australian personnel had acted "intentionally".

An English-speaking Sudanese passenger, Yousif Fasher, said he had witnessed the incident through an entry point to the wheelhouse.

He said he had then seen three of the men deliberately burned, "one after one".

"After they burn them and they take them out, they come and they call, 'Yousif, translate for anyone here. If anyone try to go to the toilet again, we will punish them like this. Tell them. Woman, in the night-time, like we told you, man at the daytime'," he said.

"This what they told, clearly, and I told the people. And people ... afraid, no-one is start to going."

Mr Ibrahim said he had not received any medical attention until he reached Indonesia, a claim backed by other passengers.

Eritrean asylum seeker Abdullah Ahmed Mohammed said he was on the roof of the wheelhouse during the burns incident.

"I am on the top … I'm [hearing] the voice 'aaagh' from the pain," he said.

Mr Mohammed said the first attempt to sabotage the engine had been when the asylum seekers had been forcibly returned to their boat.

He told the ABC that some passengers had protested against being returned to Indonesia by jumping in the water and others may have intended to sabotage the engine at the same time.

But he strenuously denied that any of the passengers had received burns from the engine while trying to sabotage it.

Passengers queried uniforms of Australian personnel

Passengers said some of the Australians involved came from a Navy ship numbered 154, which corresponds with the frigate HMAS Parramatta.

Facebook photos show the ship in December and January carrying members of a Transit Security Element, a special unit used in boarding operations.

These units are drawn from the Navy, Army and Air Force.

Riski voyage

GPS data revealed details of fishing boat Riski's more than 2,000-kilometre round trip from Indonesia to Australia and back again.

Phone video shot by the passengers during the turn-back operation shows men wearing green camouflage fatigues, which the ABC understands is normally worn by members of the Army and Air Force on these types of operations, while Navy personnel wear grey-blue camouflage.

Mr Fasher said passengers had queried the difference in uniforms among the personnel on their boat.

"When we ask them why this colour is different, they say, some of them, they say, 'we are from Navy'. Some of them said, 'we are from Army'. This is what they told us," he said.

Several passengers said they would be able to identify the Australian personnel involved in boarding their boat.

Mr Ibrahim said he would recognise the people who had burned him.

"I know their looks, if I met them I will know them," he said.

Government says burns allegations 'baseless'

The passengers said they were surprised no-one in authority in Australia had sought to interview them about their claims.

The Australian Government and military have said allegations that people were deliberately burned on the boat are "baseless" and "unsubstantiated".

He provided a statement saying: "I have repeatedly responded to questions from ABC journalists regarding outrageous claims of torture and mistreatment from those seeking to enter Australia illegally by boat in addition to claims that four people were missing at sea."